According to Article No. 129 No. 7 of the Order putting into effect the Building Standards Law of Japan, elevators are required to have installed a safety device which automatically restrains descent of the cage if the speed of the descending cage exceeds a prescribed value. A speed regulator 14 (what is sometimes called a governor) that detects the speed of cage 20 is therefore installed in the machinery room at the top of the ascent/descent path as shown in FIG. 11.
In speed regulator 14, speed regulator 14 is arranged to be rotated with ascent/descent of the cage by a means of a speed regulator rope 15 that is wound thereon with a middle part thereof connected to a safety link 17 of cage 20. The lower part of speed regulator rope 15 is wound onto a speed regulator rope tensioning pulley 16 that applies a suitable tension to speed regulator rope 15.
If a pre-set speed of speed regulator 14 is exceeded, a rope-gripping unit 19 incorporated in speed regulator 14 is actuated to grip speed regulator rope 15. Safety link 17 is thereby actuated, arresting the descent of pulling-up rods 2 of descending cage 20. That is, seen from the side of cage 20, pulling-up rods 2 ascend, causing a wedge-shaped element 3 that is linked to the bottom end of pulling-up rods 2 and is shown in detail in FIG. 12 and FIG. 13 to be also pulled up, with the result that frictional force is generated between wedge-shaped element 3 and guide rail 1, thereby effecting emergency stop of cage 20.
FIG. 12 is a front view illustrating an example of a prior art elevator emergency stop device and FIG. 13 is a cross-sectional view along B-B of FIG. 12. In FIG. 12 and FIG. 13, the upper surface of this elevator emergency stop device 18 is fixed to the bottom beam of cage 20. Also, in plan view, not shown, the framework of this elevator emergency stop device 18 is constituted by a pair of pillars, not shown, made of angle steel, welded above and below to an approximately square-shaped top plate 9A and a bottom plate 9B that is of approximately the same shape as this top plate 9A and slightly smaller than in thickness. As shown in FIG. 13, a U-shaped groove 9a into which the head of a guide rail 1 shown by the chain line fits freely is formed in the front middle part of top plate 9A and bottom plate 9B.
As shown in FIG. 12, a step 9d is formed on the under-surface at the front end on both sides of top plate 9A, and a land-shaped guide seat 9b is formed on the upper surface at the front end on both sides of bottom plate 9B. Horizontal steps 9c are formed symmetrically with steps 9d of top plate 9A described above on the outside upper surface of this guide seat 9b. 
A pair of guide plates 6 are provided on these steps 9c and 9d. Specifically, a pair of guide plates 6 are formed approximately in channel-section shape, with abutments 6a and 6b projecting on opposite sides at their top and bottom ends. Thus, abutments 6a and 6b of guide plates 6 are inserted from outside onto steps 9c and 9d and the opposite faces of guide plates 6 are inclined such that their separation becomes wider in the downwards direction.
Channel-section grooves 6c are formed on the outside of the left and right guide plates 6; as shown in FIG. 12, the two ends of a plate spring 7 made of thick sheet formed in a U-shape are freely fitted into these grooves.
A pair of pressure seats 8 are inserted beforehand from the inside at both ends of this plate spring 7. The major parts of the hemispherical portions of the heads of these pressure seats 8 are fitted into hemispherical recesses formed at the top and bottom of grooves 6c of guide plate 6, so that by pressing these hemispherical portions into the recesses by means of the restoring force of plate spring 7 the attitude of plate spring 7 is thereby maintained.
Reference numeral 2 indicates the pulling-up rods referred to above, which are made of strip-shaped steel. The bottom ends of practically trapezoid-shaped wedge elements 3 are linked through pins with the bottom ends of these pulling-up rods 2. As shown in FIG. 12, guide grooves parallel with the outside inclined faces are formed on the outer face sides of the front and rear faces of these wedge-shaped elements 3. Likewise, guide grooves shown in FIG. 12 are formed also on the front and rear faces on the opposite side of each of the guide plates 6 mentioned above.
Bent sections on both sides of a holding plate 4A formed approximately in the shape of a gutter as shown in FIG. 13 are fitted into guide grooves formed in these guide plates 6 and guide grooves formed in wedge-shaped element 3 referred to above. Shaft sections projecting at both ends of rollers SA are inserted into shaft holes at an number of locations formed on the center line of front and rear holding plates 4A.
Holding plates 4A are therefore free to move upwards together with rollers 5A by means of the bent sections thereof whereof one side is fitted into the groove formed in a guide plate 6. An identical elevator emergency stop device 18 is also provided on the other side and may further be mounted on the counter-weight.
With an elevator emergency stop device 18 constructed in this way, when the speed of descent of the cage 20 shown in FIG. 11 or counter-weight, not shown, exceeds a specified value, speed regulator rope 15 is gripped by rope gripping unit 19 of speed regulator (governor) 14. Pulling-up rods 2 are therefore arrested in advance of cage 20, causing these to be raised relative to cage 20 and guide plates 6. The wedge-shaped elements 3 that abut the bottom ends of these pulling-up rods 2 are thereby raised with respect to the cage 20 or counter-weight. When this happens, the opposite faces of the pair of wedge-shaped elements 3 are pressed against the side faces of the head of guide rail 1, causing the guide rail 1 to be gripped from both sides, thereby arresting cage 20 or the counter-weight.
The rollers 5 that are inserted in holding plates 4A that ascend together with the wedge-shaped elements 3 are incorporated in order to prevent lowering of the pressing force onto the guide rail 1, by reducing the friction between the wedge-shaped elements 3 and guide plates 6, thereby ensuring that the action of raising the wedge-shaped elements 3 takes place smoothly.
Although in general the coefficient of dynamic friction takes a fixed value determined by the material properties of the sliding members and/or the condition of the sliding surfaces etc., irrespective of the sliding velocity, in the region where the sliding velocity exceeds 10 m/s, it has been experimentally confirmed that the coefficient of dynamic friction decreases with increase in velocity.
However, with the conventional elevator emergency stop device, sliding takes place between the wedge-shaped elements and the guide rail with a pair of wedge-shaped elements being pressed on to the guide rail with a pre-set spring force i.e. always with a fixed pressing force.
Consequently, changes in the coefficient of dynamic friction are directly reflected in changes in the breaking force and in the case of a high-speed elevator capable of exceeding 10 m/s, as shown in FIG. 3A, in emergency braking using such an elevator emergency stop device, the elevator speed is high in the initial period of braking and the coefficient of friction is small. The degree of deceleration is therefore small but immediately before stopping the speed becomes slower and the frictional force becomes large, so the degree of deceleration becomes large.
In the Order implementing the Building Standards Law referred to above, a mean deceleration under emergency braking of 0.35 G to 1.0 G is laid down, so in the case of emergency braking at a speed of above 15 m/s, the deceleration immediately before stopping becomes extremely large, resulting in considerable load on the passengers.